Microscopy offers scientists and engineers a way to gain a better understanding of the materials with which they work. Under high magnification, it becomes evident that many materials (including rock and bone) have a porous microstructure that permits fluid flows. Such fluid flows are often of great interest, e.g., in subterranean hydrocarbon reservoirs. The possibility of characterizing materials in terms of porosity, permeability, and saturation is well known, but such characterizations inevitably fail at a scale where the material is too anisotropic and/or heterogeneous to be characterized as a homogeneous medium.
Naturally, it is of interest to know the size at which a sample of the material becomes representative of the whole. The smallest volume over which a given measurement can be made that yields a value representative of larger volumes is termed a representative elementary volume (“REV”). Note that the REV depends on the selected measurement.
A number of references purport to determine the REV, but suffer from one or more shortcomings including subjectivity, error, over-estimation, overly-generous search regions, overly-restrictive subvolume positioning, inability to cope with sample heterogeneity, and inapplicability of the selected measurement to the intended use of the REV (e.g., multiphase fluid flow simulation).
It should be understood, however, that the specific embodiments given in the drawings and detailed description below do not limit the disclosure. On the contrary, they provide the foundation for one of ordinary skill to discern the alternative forms, equivalents, and other modifications that are encompassed in the scope of the appended claims.